In cellular networks direct device-to-device, D2D, communication provides an option to off-load traffic from base station and core networks serving user equipments, UEs, that want to share data with each other and that are in each other's proximity.
In the case direct D2D communication takes place in spectrum assigned to a cellular network, radio resource management actions such as mode selection, network controlled scheduling and power control are typically necessary so that the direct D2D communication is under the cellular network operator's supervision and control. For example, in the case of network-assisted D2D communication, the network typically provides different types of support functions and mechanisms to identify sufficiently closely spaced UEs and to establish, maintain, and terminate D2D connections as well as to allocate transmit power and time/frequency or code resources for D2D links.
However, a well-known problem inherent to allowing direct D2D communication within spectrum used for cellular network operation is that it gives rise to new intra- and inter-cell interference situations. For example, in case of a cellular network utilizing frequency division duplex, FDD, and where the direct D2D communication scheme is based on time division duplex, TDD, due to the presence of the D2D communication links, intra-cell orthogonality may no longer be maintained. Specifically, if the D2D links use downlink, DL, resources, i.e., the DL frequency band, D2D node transmission may cause severe intra-cell interference to UEs within the same cell. In addition, the transmission from this same D2D node may generate inter-cell interference to UEs in neighboring cells. Similarly, in cases where the uplink, UL, frequency band of the cellular network is used for the direct D2D communication, the serving base station might experience severe UL interference (i.e., intra-cell interference) due to the transmissions of the D2D nodes.
Prior art solutions for controlling the intra- and inter-cell interference between the cellular and the D2D layers are based on the assumption that the radio resources and the interference are managed by a cellular network and in particular a cellular base station or access point (also called eNB in the third generation partnership project, 3GPP, Long Term Evolution, LTE, system). This is a reasonable assumption, since the cellular spectrum in all legacy systems, as well as systems allowing direct mode D2D communications in cellular spectrum are owned by a cellular operator and managed by the cellular network.
Managing the new type of intra-cell and inter-cell interference due to the presence of D2D communications is a highly non trivial task, since it involves several aspects that are specific to the new type of (namely D2D) communications. Traditional cellular methods assume that all unexpected or sudden interference can only be caused by inter-cell interferers, which is not the case in D2D communications. Secondly, traditional methods are built on the presence of a direct control channel between the base station and the user equipment, which is not the case in D2D communications during periods when the devices are engaged in direct mode D2D communications. Lastly, traditional interference methods do not assume that D2D capable devices can transmit and receive messages to one other without involving the cellular base station, which is the case in D2D communications.
Based on these premises, prior art solutions for controlling such interference situations include those where a node in the network, e.g. a base station or NodeB, dynamically controls which resource the D2D pair may use for the D2D direct communication. Such solutions have a drawback that it requires substantial network resources such as signaling and processing resources. These drawbacks increase in cases where two or more base stations, i.e. neighboring cells, become involved in the process.
In other types of D2D systems, such as ad-hoc systems utilizing Bluetooth or WiFi Direct technology, schemes for interference management build on the assumption that communicating nodes need to solve any potential interference problem without infrastructure intervention or assistance. This is because in these technologies there is typically no central entity that can help the ad-hoc nodes to properly allocate resources and manage interference. Furthermore, in these technologies there is no hierarchy among communicating nodes in terms of which device may or may not cause interference to another. Moreover, due to the fact that such ad-hoc networks operate in unlicensed spectrum they can suffer interference from other technologies or even interference sources that are completely unknown and thereby totally uncontrollable, such as household appliances and medical equipment.
In conclusion, prior art methods for managing interference in D2D systems suffer from intra-cell interference, inter-cell interference and the limitations of central handling of radio resource management.